Ink additives

ABSTRACT

An additive for a pigment based ink—jet printing composition which is used in conjunction with a printing head that comprises metallic components, is disclosed. The additive comprises a cationic component and an anionic component, and characterized in that the cationic component is a cationic surfactant. Preferred additives are those where the cationic component is C 10-22 alkyl trimethyl ammonium. Pigment-based ink—jet printing compositions comprising these additive are also described.

FIELD OF THE INVENTION

The present invention relates to ink jet printing formulations andspecifically it concerns pigment-based ink jet printing formulationsthat contain anti clogging agents.

BACKGROUND OF THE INVENTION

Ink jet printing is a well-known technique by which printing is donewithout establishing actual contact between the printing device and thesubstrate on which the printed matter is deposited. One such methodcomprises projecting a stream of droplets towards a surface, where thetrajectories of the droplets are controlled electronically, thusobtaining the desired printed image. Another method of ink jet printingis to direct droplets on demand from a set of orifices onto a substratewhich moves relatively to the set of orifices.

The ink compositions used in these devices, must meet variousrequirements concerning viscosity, surface tension, resistivity,solubility, wetability of the substrate, rapid drying and that they maypass through an ink jet orifice without crusting or clogging it. Itshould be understood that crusting and clogging these orifices isunacceptable because it reduces print quality by leaving a white,non-printed area on the substrate and ultimately leads to failure of theprinter to print. When using pigments-based inks in ink-jet printers,clogging was found to be an extremely severe problem due to extensiveclogging caused by pigment aggregation.

In the past, a number of solutions suggesting ways to improve ink jetprinting formulations, have been described.

U.S. Pat. No. 5,431,720 discloses a quick-drying ink composition whichhas good penetrating property and preservation stability, and compriseswater, a lubricant, a coloring agent and R—O(CH₂CH₂O)_(m)CH₂COOM, whereR is an alkyl group having 6 to 14 carbon atoms; M is a cation selectedfrom among alkali metal ion, quaternary ammonium cation, quaternaryphosphonium cation, alkanol amine cation, and m is an integer of 3 to12.

U.S. Pat. No. 5,102,458 discloses the incorporation of a C₂₋₄ alkylamine into a non-aqueous, ink jet printing formulations so as to inhibitcorrosion of metals which come into contact with the ink formulation

U.S. Pat. No. 5,106,417 teaches the use of an ink composition havingimproved viscosity, where this composition comprises a solid pigmentbased on a polyacrylic resin, water dilutable organic solvent such asC₁-C₄-alkanols, lower aliphatic ketones and others, water and ahumectant such as ethyleneglycol diethylene glycol triethylene glycoland the like.

U.S. Pat. No. 5,494,759 discloses an ink jet printing formulation whichcomprises a support and an ink receiving layer containing a pigment, ahydrophilic binder comprising a mixture of polyvinyl alcohol,polyvinylpyrrolidone and a vinyl acetate homopolymer and/or vinylacetate alkyl acrylate copolymer, together with a quaternary ammoniumcompound. This composition, according to U.S. Pat. No. 5,494,759 assuresa good waterfastness and web rub off properties, as well as high colordensity and image clarity.

A water soluble dye ink composition comprising an anionic dye componentand a cationic dye counter ion, where the cationic dye counter ion isselected from among lithium, a quaternary ammonium ad a quaternaryphosphonium, is disclosed in U.S. Pat. No. 5,462,592.

U.S. Pat. No. 5,169,437 discloses a possible solution to the problem ofcrusting and clogging of the orifices by employing a humectant in theaqueous ink-jet compositions. In accordance with this reference,including compounds such as ethylene glycol, propylene glycol,trimethylol propane, pentaethylene glycol, improves the ink compositionby reducing the rate of evaporation.

SUMMARY OF THE INVENTION

It is therefore the object of the present invention to provide anadditive for a pigment-based ink-jet printing composition, capable ofsubstantially reducing clogging in a printing head of an ink-jetprinter.

It is a further object of the present invention to provide apigment-based ink-jet printing composition comprising an additive whichis capable of substantially reducing clogging in the printing head andcorrosion of metal parts of the ink jet printing apparatus with whichthe printing ink composition comes into contact.

Other objects of the invention will become apparent as the descriptionproceeds.

The present invention concerns an additive for a pigment based ink-jetprinting composition which is used in conjunction with a printing headthat comprises metallic components, said additive comprising a cationiccomponent and an anionic component, characterized in that the cationiccomponent is a cationic surfactant

The term “surfactant” as used hereinafter relates to a substance that,when present at low concentration in a system has a property ofadsorbing onto surfaces or interfaces of the system and of altering to amarked degree the surface or interfacial fee energies of those surfacesor interfaces.

Ink-jet printing compositions which include pigment(s) therein, are infact dispersions of pigments, where the pigment particles demonstrate atendency to aggregate, thus clogging the ink jet orifices of theprinters print head. The purpose of the present invention is to providean additive that when added to an ordinary pigment-based ink-jetprinting composition, will retain the ink's properties while preventingthe aggregation of the pigment's particles in the ink when subjected tointeraction with the print head metallic side walls. This effect isachieved by adsorption of the long chain of the cationic surfactant tothe pigments' surface, thus providing it with extra stability whichovercomes and prevents the pigment coalescence, aggregation andconsequently the clogging of the nozzles while the pigments interactwith the printing head metallic side walls.

According to a preferred embodiment of the invention, the cationiccomponent of the additive is an ammonium surfactant, preferably,C₁₀₋₂₂alkyl trimethyl ammonium.

According to another preferred embodiment of the invention, the anioniccomponent of the additive is bromide, chloride and the like.

According to yet another preferred embodiment of the invention, theadditive is C₁₆(CH₃)₃NBr.

According to another aspect of the invention there is provided apigment-based ink-jet printing composition comprising the additive ofthe invention as described above.

According to a further preferred embodiment of the invention there isprovided a pigment-based ink-jet printing composition, in which theadditive of the invention comprises about 0.05 to about 1% by weight ofthe total composition weight, preferably from about to 0.2 to about 0.4%by weight.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 demonstrates the results obtained in a comparison test conductedto evaluate the performance of the additive of the present invention.

EXAMPLES Example 1

Three pigment-based jet-inks were compared by passing each through fourprinting heads, where each one of the heads comprised 48 nozzles. Thedetails of printing heads used, are to be found in our co-pendingapplication IL 119944, which is hereby incorporated by reference. Thefirst jet-ink was a standard solvent based magenta pigmented inksupplied by Marabu, Germany, which was also used as a basis for theother two inks (to be referred to hereinafter as “ink no. 1”). Thesecond ink tested was a modification of said ink no. 1, wherein 0.2% byweight of an anionic surfactant of the type of primary ester ofphosphoric acid (mono-tetradecyl phosphate salt) was added to ink no. 1,and the third ink tested was a composition comprising ink no. 1, towhich 0.3% by weight of C₁₆(CH₃)₃NBr was added. The additives were mixedwith the ink up to complete dissolution, prior to their use. All headsoperated throughout the test under identical conditions. The number ofnon-operating nozzles was recorded as a function of time, and when theexperiment was concluded, it was verified that all the nozzles which didnot operate, could be operative again once the clogging has beenremoved.

FIG. 1 presents the results obtained after one month of operation. Inthe performance evaluation, heads which had already been in use, weretested. Therefore, some nozzles were already clogged when the teststarted, hence the graphs presenting the number of clogged nozzles donot start from zero nozzles failed. It may clearly be seen from theFigure, that all the nozzles through which ink of the first and secondtypes were jetted, were clogged within 23 days of operation, while atthat time only about 8% of the nozzles through which ink of the thirdtype was jetted, were clogged

Example 2

A printing head type Idanit Ad162 was immersed in 6 types ofpigment-based jet-inks. The first three being those described underExample 1, whereas the other three were yellow pigment based ink, cyanpigment based ink and black pigment based ink.

It was found that when immersed in each of these inks, with theexception of ink no. 3 which comprised 0.3% by weight of C₁₆(CH₃)₃NBradditive, the heads exhibited severe pitting and corrosion of themetallic parts of the printing head which were in direct contact withthe ink. At the same time large ink aggregates (in the order of 100 to500 accumulate on the inner side walls of the printing heads after 5days from the start of the test.

When the head which was immersed in ink no. 1 to which 0.3% by weight ofC₁₆(CH₃)₃NBr was added, was examined after 21 days, none of the abovedescribed phenomena were observed

What is claimed is:
 1. A method for substantially reducing clogging andpitting in an ink-jet print head, the method comprising: adding an inkadditive to an ink comprising a non-aqueous primary solvent and aplurality of pigment particles, wherein the ink additive comprises acationic component and an anionic component, the cationic componentcomprising a cationic surfactant; and passing the ink with the inkadditive through the ink-jet print head, wherein aggregation of theplurality of pigment particles is substantially reduced and pitting ofthe ink-jet print head is substantially reduced.
 2. The method accordingto claim 1, wherein the cationic component comprises an alkyl ammoniumsurfactant.
 3. The method according to claim 2, wherein the cationiccomponent comprises C₁₀₋₂₂ alkyl trimethyl ammonium.
 4. The methodaccording to claim 1, wherein the cationic surfactant comprisesC₁₆H₃₃(CH₃)₃NBr.
 5. The method according to claim 1, wherein the inkadditive constitutes from about 0.05% to about 1% by weight of the ink.6. The method according to claim 5, wherein the ink additive constitutesfrom about 0.2% to about 0.4% by weight of the ink.